"It’s like the party is a frog slowly boiling in water, being conditioned to not be worried, to not think too hard about what’s happening around them,” Flake told The Washington Post.

“They feel at a loss about what to do because it’s the president’s party, without any doubt," he said. "So, there’s a lot of whistling by the graveyard these days.”

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Flake, who has been a longtime critic of Trump's, is in a standoff with other Senate Republicans over Trump's judicial nominees.

The Arizona Republican has refused to vote for any of them until the Senate votes on legislation that would protect Mueller, who is investigating alleged collusion between Trump's 2016 campaign and Russia.